The present invention relates to a steam turbine rotor having a connection structure for application to a steam turbine plant that includes in combination at least two of a high pressure steam turbine, an intermediate steam turbine and a low pressure steam turbine, and also relates to a method of manufacturing the steam turbine rotor.
In a typical steam turbine plant equipped with a high pressure steam turbine, an intermediate pressure steam turbine and a low pressure steam turbine, a material (metal material) of a steam turbine rotor incorporated into each turbine is selected depending on the steam conditions used, e.g., pressure, temperature, flow rate, etc. The steam turbine rotor for use in the high pressure steam turbine and intermediate steam turbine having the steam temperature of 550xc2x0 C. to 600xc2x0 C. can be made of e.g., 1%CrMoV steel (ASTM-A470, class 8) or 12%Cr steel (Japanese Patent Pub. No. SHO 60-54385). The steam turbine rotor for use in the low pressure steam turbine having the steam temperature equal to or higher than 400xc2x0 C. can be made of, e.g., NiCrMo steel (ASTM-A471, classes 2 to 7) containing 2.5% or more Ni.
In a recent steam turbine plant directed toward a larger capacity and a higher efficiency, due to the necessity for each turbine of a reduced size and weight and of a simple structure, a lot of attention is being paid to the appearance of so-called high-low pressure integrated, high-intermediate-low pressure integrated, or intermediate-low pressure integrated steam turbine rotors integrated into one piece and using the same metal material for each steam turbine including the high pressure steam turbine to the low pressure steam turbine.
Such a one-piece steam turbine rotor needs a sufficient high-temperature creep rupture strength on its high pressure high temperature side and needs a sufficient tensile strength, yield strength and toughness on its low pressure/low temperature side. This means that a single rotary shaft (rotor) requires different mechanical characteristics. Specifically, the metals used in the commercial machines are 1%CrMoVNiNb steel (e.g., Japanese Patent Pub. No. SHO 58-13608), 1.7%Ni2.25%CrMoVWNb steel (e.g., Japanese Patent Laid-open Pub. No. HEI 7-316721), etc.
Although the above described one-piece steam turbine rotors is integrally molded from the initial step of fabrication, previously separately fabricated high, intermediate and low pressure steam turbine rotors may be joined together by bolts (e.g., Japanese Patent Laid-open Pub. No. SHO 62-189301) or may be welded together.
The steam turbine rotor having the welded structure is classified into two types depending on the step to weld each steam turbine rotor. One is obtained by the welding in the process of the steam turbine rotor manufacturing steps and the other is obtained by the mutual welding after the completion of manufacture of each steam turbine rotor.
For the manufacture of the former, a plurality of ingots are roughly forged, welded together and then finish forged, which is disclosed in e.g., Japanese Patent Laid-open Pub. No. SHO 53-147653.
For the manufacture of the latter, the steam turbine rotors formed from dissimilar metal of different components and compositions are welded together, which is disclosed in e.g., Japanese Patent Laid-open Pub. No. SHO 57-176305.
It has hitherto been common for the high pressure, intermediate pressure and low pressure steam turbine rotors to provide a disk-structure (in which the steam turbine rotors each has an sliced disk shape so that they are laid one on top of the other) for the welded connection thereof. In this case, the steam turbine rotors formed from the same metal of the same components and compositions are welded and connected without welding the ones made of the dissimilar metal of different components and compositions.
Use of ESR (electroslag remelting) process is proposed as the other connection method to be effected during the steam turbine rotor manufacturing steps.
This connection method can include some approaches, i.e., immediately after the electroslag melting of one consumable electrode, the other consumable electrode may be subjected to the electroslag melting, with the resultant two parts being joined together for integral molding (e.g., Japanese Patent Pub. No. SHO 53-42446), a plurality of ingots of different components and compositions may be connected together for being remelted as the ESR electrode (e.g., Japanese Patent Pub. No. SHO 56-14842), or with a view to reducing the pool depth at the center, hollow electrodes may be connected together for ESR (e.g., Japanese Patent Laid-open Pub. No. HEI 6-155001).
In this manner, a number of connection means have been disclosed for the conventional steam turbine rotors, and some of them have been adopted for the commercial machines.
The recent steam turbine plant has a trend toward enhancement on the reduced size and weight as well as the simplified structure, and from this viewpoint, investigation is directed to the high-low pressure, high-intermediate-low pressure or intermediate-low pressure steam turbine rotors.
The conventional steam turbine rotors are formed from metals of components and compositions which have been developed in conformity with the steam conditions such as the steam temperature and pressure of the individual steam turbines, i.e., high pressure, high-intermediate pressure, intermediate pressure and low pressure steam turbines. Thus, intact application of those metals of the components and compositions to the high-low pressure, high-intermediate-low pressure and intermediate-low pressure steam turbines would pose deficiencies which follow.
(1) The 1%CrMoV rotor has a good performance in the creep rupture strength within the high-temperature region of the order of 550xc2x0 C., although it may not necessarily present a sufficient tensile strength and toughness within the low temperature region and may possibly undergo a ductile fracture, a brittle fracture, etc. As the prevention measures against those, it is necessary to reduce the stress which may occur at the low-pressure part of the steam turbine rotor. However, the reduction of the stress occurring at the low-pressure part may restrict the length of the turbine blades disposed at the turbine stages, to consequently make it difficult to enhance the power plant capability.
In spite of its excellent high-temperature creep rupture strength, it would be insufficient for the higher temperature (approx. 600xc2x0 C. ) and higher pressure steam at the turbine inlet, which is required to achieve an improved efficiency in the recent power plant.
(2) The 12%Cr rotor could satisfy the above turbine inlet steam conditions due to its superior characteristics in the high temperature creep rupture strength to the 1%CrMoV steel rotor, but it presents an insufficient toughness. As a countermeasure against this fact, the length of the turbine blades disposed at the low pressure turbine stages is restricted, in the same manner as the case of the 1%CrMoV rotor.
(3) The NiCrMoV steel rotor is advantageous in the tensile strength and toughness within the low temperature region, but it may fail to present a sufficient creep rupture strength therewithin. Thus, its use in the high pressure steam turbine or intermediate pressure steam turbine may restrict the rise of the steam temperature at the turbine inlet due to its insufficient strength, making it difficult for the power plant to achieve an improved efficiency.
In this manner, when attempting to impart the increased capacity and higher efficiency to the steam turbine plant, especially, by use of the high temperature and high pressure steam with the turbine blade of a larger length incorporated therein, many restrictions have been imposed on the conventional high-low, high-intermediate-low and intermediate-low pressure integrated steam turbine rotors formed from the same material (metal material) such as the heat resisting steel.
Nevertheless, small-sized steam turbines with a small power output have used high-low, high-intermediate-low and intermediate-low pressure integrated steam turbine rotors formed from the same metal of the same components and compositions. In order to improve the steam turbine performances and enlarge the output range, however, it is necessary to increase the length of the turbine blade at the last turbine stage. In fact, increase of the turbine blade length may result in the increased centrifugal force due to rotations, and an extremely large stress may occur in the steam turbine rotor. To deal with this increased stress, the steam turbine rotor needs to have a further improved tensile strength, yield strength and toughness at the last turbine stage and its peripheries.
Moreover, the turbine blade at the last turbine stage may be made of titanium in place of the conventional steel with a view to reducing the costs and centrifugal force. Due to its elongated shape, however, the titanium turbine blade will not contribute to the reduction of the centrifugal force than expected. For this reason, the steam turbine rotor is still subjected to a large stress.
Thus, there is a need to acquire an even superior tensile strength, yield strength and toughness as well as to keep the creep rupture strength at a high temperature. In the state of the art, however, the integral steam turbine rotor have not yet been realized that is made of the same components and compositions and is capable of satisfying the need for steam turbines for the high-low pressure, high-intermediate-low pressure and intermediate-low pressure.
As a substitute for the high-low, the high-intermediate-low pressure integrated steam turbine rotor made of the same components and compositions, combination of the steam turbine rotors made of dissimilar metal would be conceivable. A bolting method is an example thereof. However, the bolting method is disadvantageous in the simplification of the structure and the reduction of weight of the steam turbine, since it needs the provision of flanged portions for fastening by means of bolts or bolt/nut pairs and needs the provision of a larger gap than the design proper value between wheels clamping the fastened portion of the steam turbine. Furthermore, the repetition of the start and stop operations of the steam turbine may cause a reduction of bolt fastening force, i.e., a so-call bolt loosening phenomena, which may possibly bring about steam turbine rotor vibrations.
Weld connection means would also be conceivable as means for connecting the steam turbine rotors made of the dissimilar metal together. In case of the weld connection means in the course of the steam turbine rotor manufacturing steps, when the rotors are extended radially and axially in the subsequent finish forging process, technical difficulties may be posed on the uniform distribution of the circumferential chemical components and compositions with a high accuracy. It may possibly cause any distortion (bend) of the steam turbine rotor in the subsequent heat treatment process or in operation. Thus, practical use thereof has not yet been achieved.
Description will then be made of weld connection means of dissimilar metal after the completion of manufacture of the steam turbine rotor. As set forth hereinabove, it has hitherto variously been put into practice to forge rotors each made of the same components and compositions such as the high pressure steam turbine rotor, intermediate pressure steam turbine rotor, high-intermediate-low steam turbine rotor and low pressure steam turbine rotor, into a disk shape and to weld them (similar material welding) to make a finished steam turbine rotor. However, practical use has not yet been made of the weld connection means for the steam turbine rotors made of dissimilar metal material of the different chemical components and compositions. Some factors therein will be conceivable.
First, it is conceived in case of the weld connection of the dissimilar metal that the welding residual stress at the weld joint tends to become larger and uneven due to the difference in values of the physical property such as the coefficient of linear expansion or thermal conductivity attributable to the difference of the chemical components and compositions of the rotor. As a result, there may occur risks of an increase in the sensitivity to SCC (stress corrosion cracking) at the weld joint and of an increase in the stress concentration at the weld Uranami (uranami) portion. A volume of pads are needed due to the increased amount of distortion of the rotor incurred by the weld, thus resulting in an increase of the rotor fabrication costs and of the number of cutting steps leading to a rise of the costs. Vibration problems may also possibly occur owing to the thermal bending in operation.
It is also envisaged due to the dissimilar metal welding that a complicated residual stress component distribution may appear at the weld joint, which may in turn incur an enhanced sensitivity to SCC.
From the common sense that the conventional high-quality steam turbine rotor should have as high a uniformity as possible at every portions irrespective of its dimensions, it would also be envisaged in case of the dissimilar metal weld connection means that the strength of the low pressure rotor at its connecting portion may lower after PWHT (postweld heat treatment) since PWHT temperature may not reach a proper value for the two steam turbine rotors to be connected together.
Assumption is such that the above-described various factors in the dissimilar metal weld connection means have impeded so far the practical use of the steam turbine rotors having the dissimilar metal weld connection structure.
Other bonding means for the dissimilar metal rotors could be a utilization of ESR (Electro Slag Refining) process. This is a process intended to axially graduate the chemical components and compositions by bonding the dissimilar metals together in the melting and solidification steep of the steam turbine rotor, which may incur a technical difficulty in imparting a circumferentially uniform distribution to the chemical components and compositions, rendering the technique impractical.
The present invention was conceived in view of the above background arts. It is therefore the object of the present invention to provide a steam turbine rotor and a method of manufacturing the same, capable of relieving the residual stress at the weld portions with appropriate components and compositions, in addition to the reduction of weight, in forming a one-piece turbine rotor for high-low pressure steam turbine, high-intermediate-low pressure steam turbine or intermediate-low pressure steam turbine through mutual connections of the dissimilar metal steam turbine rotors, the steam turbine rotor being capable of suppressing the sensitivity to stress corrosion cracking (SCC) or the bending distortion of the steam turbine, of ensuring the strength or other qualities through the sufficient postweld heat treatment (PWHT), and of sufficiently dealing with the elongated turbine blade required to meet with the demand for the increased capacity and higher efficiency of the steam turbine.
In order to attain the above object, according to a first aspect of the present invention there is provided a steam turbine rotor comprising in combination at least one of high pressure rotor and an intermediate pressure rotor and a low pressure rotor, wherein the at least one of the high pressure rotor and the intermediate pressure rotor and the low pressure rotor is formed from metal materials of different chemical compositions and being welded together by use of welding means. The high pressure rotor may be formed from 1%CrMoV steel. The low pressure rotor may be formed from 3 to 4%NiCrMoV steel. The intermediate pressure rotor may be formed from 1%CrMoV steel.
In order to achieve the above object, according to a second aspect of the present invention there is provided a steam turbine rotor comprising in combination at least one of a high pressure rotor and an intermediate pressure rotor and a low pressure rotor, wherein a high pressure turbine first stage of the high pressure rotor and an intermediate pressure turbine first stage of the intermediate pressure rotor are made of 12%Cr steel, all other high pressure turbine stages of the high pressure rotor than the high pressure turbine. first stage are made of 1%CrMoV, with all other intermediate pressure turbine stages of the intermediate pressure rotor than the intermediate pressure turbine first stage being made of 1%CrMoV, and the low pressure rotor is formed from 3-4% NiCrMoV steel, the rotors being joined together by use of welding means. The 1%CrMoV steel may contain 0.8 to 1.3 wt % of Cr, 0.8 to 1.5 wt % of Mo, 0.2 to 0.3 wt % of V and remaining parts of Fe or others. The 3-4%NiCrMoV steel may contain 2.5 to 4.5 wt % of Ni, 1.5 to 2.0 wt % of Cr, 0.3 to 0.8 wt % of Mo, 0.08 to 0.2 wt % of V and remaining parts of Fe and others. The rotor using 12%Cr steel may be shaped to have either one of a convexed end and a concaved end. The rotor using 1%CrMoV steel may be shaped to have the other of a convexed end and a concaved end, and the rotor using 12%Cr steel may be fitted to the rotor using 1%CrMoV steel and is welded thereto by use of the welding means. The convexed end and the concaved end may be inclined relative to a central axis. Preferably, a weld metal for use as the welding means contains 2.7 to 3.5 wt % of Ni, 0.2 to 0.5 wt % of Cr, 0.4 to 0.9 wt % of Mo, and remaining parts of Fe and others. After welding the high pressure rotor and/or the intermediate pressure rotor and the low pressure rotor together by use of the welding means, a turbine stage region of the high pressure rotor and/or of the intermediate pressure rotor and a turbine stage region of the low pressure rotor excepting a last turbine stage thereof may be subjected to a heat treatment by use of heat treatment means. After welding the high pressure rotor, the rotor using 12%Cr steel, the intermediate pressure rotor and the low pressure rotor together by use of the welding means, a turbine stage region excepting a last turbine stage of the high pressure rotor, the rotor using 12%Cr steel, the intermediate pressure rotor and the low pressure rotor may be subjected to a heat treatment by use of heat treatment means.
In order to attain the above object, according to a third aspect of the present invention there is provided a steam turbine rotor having in combination at least one of high pressure rotor and an intermediate pressure rotor and a low pressure rotor, the steam turbine rotor comprising a narrow gap formed at split mating surfaces extending transversely across a center bore of each of the rotors; and a laser displacement measuring sensor and a laser measuring meter which, upon welding the narrow gap, detect a displacement of each rotor arising from welding heat and a displacement of the narrow gap of the split mating surfaces, to provide a control of increase and decrease in the amount of heat input from a welding torch.
In order to attain the above object, according to a fourth aspect of the present invention there is provided a steam turbine rotor having in combination a high pressure rotor and/or an intermediate pressure rotor and a low pressure rotor, the steam turbine rotor comprising a narrow gap formed at split mating surfaces extending transversely across a center bore of each of the rotors, and submerged arc welding means arranged to weld the narrow gap. The narrow gap may have an angle of inclination of 10/100 relative to a traverse line intersecting a center axis of the rotor. The split mating surfaces may have a hollow portion formed toward the center bore.
In order to attain the above object, according to a fifth aspect of the present invention there is provided a steam turbine rotor having in combination a high pressure rotor and/or an intermediate pressure rotor and a low pressure rotor, the steam turbine rotor comprising an overlay weld joint formed toward a center bore at a weld end after welding the split mating surfaces that extend transversely across the center bore of each of the rotors.
In order to attain the above object, according to a sixth aspect of the present invention there is provided a steam turbine rotor having in combination a high pressure rotor and/or an intermediate pressure rotor and a low pressure rotor, the steam turbine rotor comprising a residual stress portion formed toward a center bore at a weld end by use of a blaster means after welding the split mating surfaces that extend transversely across the center bore of each of the rotors.
In order to attain the above object, according to a seventh aspect of the present invention there is provided a steam turbine rotor having in combination a high pressure rotor and/or an intermediate pressure rotor and a low pressure rotor, the steam turbine rotor comprising an anticorrosion coated portion formed toward the external surface of a weld end after welding the split mating surfaces that extend transversely across the center bore of each of the rotors.
In order to attain the above object, according to an eighth aspect of the present invention there is provided steam turbine rotor having in combination a high pressure rotor and/or an intermediate pressure rotor and a low pressure rotor, wherein after welding the high pressure rotor and/or the intermediate pressure rotor and the low pressure rotor together, a turbine stage region of the high pressure rotor and/or the intermediate pressure rotor and a turbine stage region of the low pressure rotor excepting a last turbine stage thereof are subjected to a heat treatment at a temperature lower than a tempering temperature of either one of the high pressure rotor and the intermediate pressure rotor, a temperature higher than a tempering temperature of the low pressure rotor and a temperature lower than an Acl transformation temperature of the low pressure rotor.
In order to attaint the above object, according to a ninth aspect of the present invention there is provided a method of manufacturing a steam turbine rotor comprising the steps of welding together a turbine first stage rotor 12%Cr steel for use as a high pressure turbine first stage and an intermediate pressure turbine first stage, a high pressure rotor 1%CrMoV steel for use as other turbine stages than the high pressure turbine first stage, an intermediate pressure rotor 1%CrMoV steel for use as other turbine stages than the intermediate pressure turbine first stage and a low pressure rotor 3-4%NiCrMoV steel; and thereafter, subjecting a turbine stage region of the turbine first stage rotor 12%Cr steel, the high pressure rotor 1%CrMoV steel and the intermediate pressure rotor 1%CrMoV steel as well as a turbine stage region excepting a final turbine stage of the low pressure rotor 3-4%NiCrMoV steel to a heat treatment at a temperature lower than a tempering temperature of eithier one of the 12%Cr steel and the 1%CrMoV steel, a temperature higher than a tempering temperature of the 3-4%NiCrMoV steel and a temperature lower than an Acl transformation temperature of the 3-4%NiCrMoV steel. The temperature of the heat treatment is preferably within a range of 600 to 650xc2x0 C.
According to the steam turbine rotor and its manufacturing method of the present invention, as set forth hereinabove, appropriate metals were used under environmental conditions of high temperature/high pressure and low temperature/low pressure, and when welding rotors of dissimilar metals together, appropriate measures were taken with the reduced weight and appropriate postweld heat treatment, thereby making it possible to secure an excellent creep rupture strength under the high temperature/high pressure environment and simultaneously to secure an excellent room temperature tensile strength and toughness under the low temperature/low pressure environment, as well as making it possible to suppress the SCC sensitivity and suppress the residual stress at the weld joint as low as possible, thus ensuring a sufficient application to the turbine blade having an increased length.
Thus, the steam turbine rotor and its manufacturing method in accordance with the present invention can fully deal with an increase of steam conditions used and with an increased length of the turbine blade for use at the last turbine stage of the low pressure steam turbine, whereby it is possible to realize a large-capacity and high-efficiency steam turbine plant.
The nature and further characteristic features of the present invention will be made more clear from the following descriptions made with reference to the accompanying drawings.